Microphonic behavior is an electrical response induced by acceleration that comes from mechanical stimulus. Various physical phenomena, such as vibrations, pounding and acoustic pressure, can create the mechanical stimulus from which Microphonic behavior comes. In electronic equipment, mechanical vibrations, or mechanical modulations, can come from a very high speeds movement, exposure to sound pressure waves or exposure to the elements such as heavy rain or hailstones. For example, when hailstones pound the cover of an enclosed system the cover vibrates if it is thin and flexible, and it may also produce sound pressure waves because of the drum effect. These sound pressure waves are conducted through the air in the cavity of the enclosure and create mechanical vibrations.
When in a high vibrations environment, electronic components tend to exhibit microphonic behavior by transforming the mechanical vibrations into an electrical signal. This transducer-like behavior introduces the electrical signal into the electronic equipment as undesirable noise.
In communication systems, the undesirable noise can disrupt the communication medium and result in bit errors or synchronization loss. Loss of synchronization causes large burst of data errors. This means that for a short period of time, the communication may be totally lost until the system is resynchronized. For a high quality communication link, large bursts of data errors are unacceptable.
Microwave components are often more susceptible to microphonic behavior. When the mechanical vibrations are considerable relative to the electrical wavelength they produce microphonic sensitivity, and this sensitivity increases as the wavelength shortens. For instance, microphonics can detune microwave circuits and such detuning is more sensitive to mechanical modulations of the electrical wavelength. The higher the frequency the more microphonic sensitive the microwave systems become.
Moreover, in wireless communication systems such as microwave radio, microphonics has some correlation with the modulation scheme and transmitted data rate. In systems with quadrature amplitude modulation (QAM), for example, as the modulation level increases and as the carrier recovery loop bandwidth narrows, the system becomes more susceptible to microphonics. Thus, conventional microwave radio systems using QAM may pass microphonic specification on 128 QAM, 75E1 but nevertheless fail the specification on 128QAM, 16DS1 (75E1 is a European transmission standard, ETSI, of 2.048 Mbits/sec×75; 16DS1 is a U.S. transmission standard, ANSI, of 1.544 Mbits/sec×16). It is more desirable to have microwave communication systems that satisfy the specifications of both standards, however.
Therefore, there is need to consider the potential for microphonic behavior in system design. One desired aspect of such system design might be to substantially reduce microphonic behavior and/or its effects.